My wife’s 103-year-old grandmother lived in a third floor walk-up apartment in New York City. Every day she walked up and down those stairs several times to go shopping, to the post office, the dry cleaner’s and do other little errands. At 103, she was as sharp as a tack. She never forgot a birthday, an anniversary or a single holiday. And God forbid you forgot to send her a card or call her on her birthday — you’d hear about it for ages. The exercise she got on those stairs and errands may not only have protected her heart so she could live past 100, it may also have protected her brain.

Walking is one of the safest and easiest ways to get an aerobic workout. How much walking or exercise each person needs depends on their baseline fitness level, age and other health factors. And getting short amounts of cardio workouts throughout the week is more effective than being a weekend warrior who only exercises on Saturday and Sunday.

In a study of more than 18,000 older women, Harvard researchers found that 90 minutes a week of brisk walking, or approximately 15 minutes a day, was all one needed to delay cognitive decline and reduce possible risk for future Alzheimer’s disease. University of Pittsburgh scientists found that the more that older people walked, the better their cognitive abilities and the larger their brain. A larger brain is associated with a lower risk for Alzheimer’s disease.

Equally convincing evidence of the brain benefits of physical exercise comes from studies that have monitored volunteers in exercise programs and compared them to sedentary control groups. Dr. Arthur Kramer and colleagues at the University of Illinois recruited volunteers aged 58 to 77 years, and assigned them to either a walking group or a group that did stretching and toning. After six months, the walkers had increased blood flow in brain circuits controlling spatial ability and complex thinking, compared with the stretching and toning group. Although stretching and toning are important components of a comprehensive physical fitness program, Professor Kramer’s findings demonstrate the added value of cardiovascular conditioning for maintaining brain health.

Aerobic conditioning may be improving our mental acuity in several ways. Exercise gets the heart pumping more blood to the brain, which appears to reverse cellular deterioration associated with aging. It also stimulates the growth of new synapses — the connection sites between neurons — and makes brain cells more responsive to external stimuli.